Articles comprising fibres and/or fibrids, fibres and fibrids and production method of same

ABSTRACT

The invention relates specifically to novel articles and, in particular, to non-woven articles comprising fibres and/or fibrids. The invention also relates to novel fibres and fibrids and to a method of producing said fibres and fibrids.

The present invention relates to novel articles, especially non-wovenarticles comprising fibres and/or fibrids. It also relates to novelfibres and fibrids and to a process for obtaining these fibres andfibrids.

Particularly in the electrical insulation field, the aim is to obtainproducts exhibiting good temperature resistance and good mechanicalproperties and/or dielectric properties. These products may, forexample, be non-woven articles produced from thermally stable fibres. Insuch an article, good cohesion of the thermally stable fibres isnecessary for obtaining a good level of mechanical properties, or indeedalso a uniform and dense structure of the article in order to obtaindielectric properties. For this purpose, the aim is to obtain goodcohesion of the thermally stable fibres within the article. The aim isalso to obtain a uniform and compact structure within the article. Thesearticles, depending on their structure (especially their density) and/ortheir formulation, may have a mechanical and/or dielectric reinforcementfunction.

Document U.S. Pat. No. 2,999,788 proposes, for example, the preparationof synthetic polymer particles or “fibrids” having a particularstructure, that can be used with fibres based on synthetic polymers, forthe production of coherent fibrous structures by a papermaking process.A hot-pressing operation may be carried out on these structures, causingthe fibrids to undergo plastic flow. However, the preparation of suchfibrids, carried out by precipitation in a sheared medium, iscomplicated and expensive. These fibres must also remain in aqueousmedium in order to be used directly. Consequently, they can neither beisolated nor transported easily, which limits their use.

Document FR 2 163 383 proposes to prepare non-woven articles formed by aweb of fibres based on a non-melting material or one having a meltingpoint above 180° C., the fibres being bonded together by means of apolyamide-imide bonding agent used in a proportion of 5 to 150% of theweight of dry fibres employed. However, the impregnation with resin iscarried out in solution in a solvent, which consequently has deleteriouseffects on the characteristics of the non-wovens.

To improve the feasibility of non-woven webs, document FR 2 156 452proposes to prepare non-woven webs by a wet route, the webs being formedfrom fibres made of a non-melting material or one having a melting pointabove 180° C., bonded together by a thermoplastic polymer in powderform.

Although in theory these webs can be obtained by a papermakingtechnique, industrial production of such webs is in fact difficult: thisis because the compound comprising synthetic fibres and resin-basedbonding agent has too low a cohesion to be able to be handled and inparticular such a compound has insufficient cohesion to be able to beprepared dynamically, for example on a commercial papermaking machine;such webs are mainly able to be produced on laboratory apparatuses ofthe “Formette Franck” type, that is to say in a static and batch manner,as is apparent from the examples.

Document FR 2 685 363 proposes the wet preparation of a paper formedfrom fibres having a thermal withstand greater than or equal to 180° C.,the fibres being bonded together by means of a fibrous bonding agent anda chemical bonding agent.

The use of bonding agents for ensuring fibre cohesion in articles, forexample non-woven articles in particular poses difficulties and incurscosts as regards the use of these bonding agents.

The present invention provides novel articles, especially non-wovenarticles, not having the above drawbacks, comprising fibres and/orfibrids. The invention also provides novel fibres and fibrids, and aprocess for obtaining these fibres and fibrids, and articles obtainedfrom these fibres and fibrids, such as non-woven articles. Thethermoplastic part of the fibre or fibrid of the invention acts inparticular as the chemical bonding agent described above. In particular,it has the property of “undergoing plastic flow” under a compressivestress and temperature stress. This thus ensures the cohesion of thethermally stable fibres in these articles and their level of thermal andmechanical properties is very satisfactory. These articles may have adense uniform structure, and therefore a good level of dielectricproperties.

For this purpose, the first subject of the invention is an articlecomprising at least fibres and/or fibrids, characterized in that thefibres and fibrids are formed from a polymer blend comprising at least:

-   -   A thermally stable polymer; and    -   A thermoplastic polymer chosen from the group of polysulphides        and polysulphones.

The second subject of the invention is a fibre and a fibrid such asthose described above and a process for obtaining them.

In a third subject, the invention proposes the use of the articles asdescribed above in the field of electrical insulation.

The thermally stable polymer of the invention is preferably anon-melting polymer or one having a glass transition temperature above180° C., preferably greater than or equal to 230° C., or higher. Thethermally stable polymer of the invention has a long-term thermalwithstand (that is to say capability of retaining in particular itsphysical properties) at a temperature above 180° C. This thermallystable polymer is preferably chosen from polyaramids and polyimides.Mention may be made, as examples of polyaramids, of aromatic polyamides,such as the polymer known by the brand name Nomex®, or polyamide-imides,such as the polymer known by the brand name Kermel®. As an example ofpolyimides, mention may be made of the polyimides obtained according todocument EP 0 119 185, known by the brand name P84®. The aromaticpolyamides may be as described in Patent EP 0 360 707. They may beobtained using the process described in Patent EP 0 360 707.

The thermoplastic polymer is chosen from the group of polysulphides andpolysulphones. As an example of a polysulphide, mention may be made ofpolyphenylene sulphide denoted hereafter by PPS. As an example ofpolysulphones, denoted hereafter by PSU, mention may be made ofpolyethersulphone denoted hereafter by PESU or polyphenylenesulphonedenoted hereafter by PPSU.

These thermoplastic polymers have a glass transition temperature of lessthan or equal to 250°, thereby allowing them to act in particular aschemical bonding agent in the articles of the invention and allowingthem to undergo “plastic flow” under a compressive stress andtemperature stress. These polymers also have good thermal stability,since they belong to a thermal class (thermal index) above 130°. This isadvantageous for obtaining articles exhibiting good thermal stability.

According to a preferred embodiment of the invention, the thermoplasticpolymer and the thermally stable polymer are soluble in the samesolvent. Advantageously, the solvent is an aprotic polar solvent. It ismore preferably chosen from DMEU, DMAC, NMP and DMF.

Advantageously, the fibre or fibrid according to the invention comprisesat least 10% by weight of thermoplastic polymer.

Fibrids are small non-granular fibrous particles or particles in theform of films that are not rigid. Two of their three dimensions are ofthe order of a few microns. Their small size and their flexibility allowthem to be deposited in physically interlaced configurations, such asthose commonly found in papers formed from pulp.

The fibre according to the invention preferably has a linear density ofbetween 0.5 dtex and 13.2 dtex. The fibre of the invention preferablyhas a length of between 1 and 100 mm.

The fibre according to the invention may have varied cross-sectionalshapes, such as a round, trilobate or “flat” shape. The term “fibre offlat cross-sectional shape” is understood to mean a fibre whoselength/width ratio is greater than or equal to 2.

The fibre or fibrid according to the invention may be treated with asize.

According to one particular embodiment of the article of the invention,the fibres are obtained by blending the thermally stable polymer withthe thermoplastic polymer, followed by spinning the blend.

Any means known to those skilled in the art for blending two polymersmay be used. Preferably, the polymers are blended by dissolving thepolymers in at least one common solvent. The thermoplastic polymer andthe thermally stable polymer may be dissolved together, simultaneouslyor in succession, in a solvent or a mixture of mutually misciblesolvents, for example in a single reactor. The polymers may also bedissolved separately in the same solvent or in different solvents thatare mutually miscible, for example in two different containers, and thenthe polymer solutions are mixed together.

The dissolution conditions, such as the temperature, are determined bythose skilled in the art according to the nature of the polymers and thesolvent(s) that is (are) used. The dissolution may, for example, becarried out hot, with stirring, in order to facilitate the dissolution.

The dissolution may be carried out at room temperature. Preferably, thedissolution temperature is between 50 and 150° C.

The dissolving solvent(s) is (are) advantageously aprotic polarsolvents. It is possible to use a dimethylalkylene urea, for exampledimethylethylene urea (DMEU) or dimethylpropylene urea. Preferably, itis chosen from DMEU, dimethylacetamide (DMAC), N-methylpyrrolidone (NMP)and dimethylformamide (DMF). The dissolving solvent may be a mixture ofaprotic polar solvents, for example a mixture of dimethylethylene ureaand an anhydrous aprotic polar solvent, such as NMP, DMAC, DMF,tetramethyl urea or γ-butyrolactone.

The polymer solution obtained after dissolution is called collodion. Thesolution obtained is preferably clear.

The total concentration by weight of the polymers relative to thesolution is preferably between 5 and 40%.

The solution may also include additives, such as pigments, reinforcingagents, stabilizers and delustrants.

The solution must also have a viscosity allowing it to be spun,generally between 100 and 1000 poise. For wet spinning, the viscosity ispreferably between 400 and 800 poise, measured by means of a viscometerknown by the brand name EPPRECHT RHEOMAT 15. For dry spinning, theviscosity is preferably between 1500 and 3000 poise.

The polymer blend may also be produced in-line during the spinning step,for example by the in-line injection of each polymer, whether or notdissolved in a solvent, during the spinning process.

Any method of spinning a polymer blend, especially a polymer solution,known to those skilled in the art may be used here within the context ofthe invention.

Mention may be made, for example, of dry spinning, in which the polymersolution (fibre-forming substance in the dissolved state) is extrudedthrough capillaries in an environment favourable for the removal of thesolvent, for example in an evaporating atmosphere maintained at atemperature close to or above the boiling point of the solvent, allowingthe filaments to solidify. The filaments leaving the evaporating chamberare stripped of their residual solvent. To do this, they may be washedwith water, optionally boiling water under pressure, and then they areusually dried, preferably at a temperature above 80° C. They may also beheat-treated at a temperature greater than or equal to 160° C. underreduced pressure and/or in an inert atmosphere. After having beenstripped of their residual solvent, they may be drawn, for example at atemperature above 250° C., preferably greater than 300° C., preferablyin the absence of oxygen.

According to one particular embodiment of the invention, the spinningmethod is a wet spinning method, in which the polymer solution (solutionof fibre-forming substances) is extruded into a coagulating bath.

The temperature of the spinning solution may vary widely, depending onthe viscosity of the solution to be spun. For example, a solution havinga low viscosity may be easily extruded at ordinary temperatures, whereasfor a solution having a high viscosity, it is preferable for this to beextruded hot, for example at 120° C. or even higher, so as to avoidexcessively high pressures in the die. The spinning solution isadvantageously maintained between 15 and 40° C., preferably between 15and 25° C.

The coagulating bath used in the process according to the invention ispreferably an aqueous solution containing from 30 to 80% by weight,preferably from 40 to 70% by weight, of a solvent or solvent mixture,preferably a dimethylalkylene urea (DMAU) or DMF, or a mixture thereof,although it is often advantageous to use a bath containing more than 50%by weight of solvent in order to obtain filaments having betterdrawability, and therefore better final properties.

Preferably, the polymers of the solution to be spun have similarcoagulation rates.

The spinning rate in the coagulating bath may vary widely, depending onits solvent concentration and the distance that the filaments travelthrough this bath. This spinning rate in the coagulating bath may bereadily chosen to be between, for example, 10 and 60 m/min, althoughhigher rates can be achieved. It is generally not advantageous to spinat lower rates for process efficiency reasons. Moreover, excessivelyhigh spinning rates in the coagulating bath reduce the drawability ofthe filaments in air. The spinning rate in the coagulating bath willtherefore be chosen to take into account both the efficiency and thedesired properties of the finished filament.

The filaments leaving the coagulating bath in the gel state are thendrawn, for example in air, with a draw ratio defined by (V₂/V₁)×100, V₂being the velocity of the drawing rolls and V₁ that of the feed rolls.The draw ratio of the yarns in the gel state is greater than 100%,preferably greater than or equal to 110% or even higher, for examplegreater than or equal to 200%.

After drawing, preferably in air, generally carried out by passagebetween two series of rolls, the residual solvent is removed from thefilaments by known means, generally by means of a washing operationusing water flowing countercurrently, or on washing rolls, preferably atroom temperature.

According to another particular embodiment of the invention, thespinning method is a dry spinning method.

In the two spinning processes described above (dry spinning and wetspinning), the washed filaments are then dried by known means, forexample in a dryer or over rolls. The temperature of this drying mayvary widely, as may the drying rate, which is higher the higher thetemperature. It is generally advantageous to carry out drying with aprogressive rise in the temperature, this temperature possibly reachingand even exceeding 200° C. for example.

The filaments may then undergo hot overdrawing, in order to improvetheir mechanical properties and in particular their tenacity, which maybe beneficial for some applications.

This hot overdrawing may be carried out by any known means: oven, plate,roll, roll and plate, preferably in a closed chamber. It is carried outat a temperature of at least 150° C., possibly a temperature of up to oreven exceeding 200 to 300° C. The overdraw ratio is generally at least150%, but it may vary widely depending on the desired properties of thefinished yarn. The total draw ratio is therefore at least 250%,preferably at least 260%.

The combination of drawing and possibly overdrawing may be carried outin one or more stages, continuously or batchwise, with the aboveoperations. Furthermore, the overdrawing may be combined with drying. Todo this, all that is required is to provide, at the end of drying, ahigher temperature zone for the overdrawing.

The filaments obtained are then chopped into fibres using a method knownto those skilled in the art.

According to another embodiment of the article of the invention thefibrids are obtained by blending the thermally stable polymer with thethermoplastic polymer, followed by precipitation of the blend under ashear stress.

The thermally stable polymer/thermoplastic polymer blend may be producedin a manner similar to that described above for the fibres.

The fibrids of the invention may especially be obtained by precipitatinga polymer solution in a fibridizing apparatus of the type described inU.S. Pat. No. 3,018,091, in which the polymers are sheared while theyare precipitating.

According to a particular embodiment of the invention, the articles arenon-woven articles. The non-woven articles are in the form of sheets,films or felts, and in general they define any coherent fibrousstructure not involving any textile operation, such as spinning,knitting or weaving.

The article may be obtained from a single type of fibre or on thecontrary from blends of fibres. The non-woven article of the inventioncomprises, at least in part, fibres and/or fibrids according to theinvention. The article of the invention may comprise fibres of differentkinds and/or fibrids of different kinds. Apart from the fibres and/orfibrids according to the invention, the non-woven article may comprise,for example, thermally stable or reinforcing fibres and/or fibrids ofthe para-aramid type, meta-aramid type, polyamide-imide type, etc.

The non-woven article may comprise, for example, fibres according to theinvention and thermally stable fibres. If the article comprises fibrids,the article may, for example, comprise fibres according to the inventionand fibrids of thermally stable polymer according to a first embodiment;or the article, may, for example, comprise thermally stable fibres andfibrids according to the invention according to another embodiment.

The non-woven article of the invention may be obtained by a method andan apparatus for preparing a non-woven article that are known to thoseskilled in the art. The article of the invention is generally obtainedby carrying out a “web-forming” step, that is to say a step in which thefibres and/or fibrids are spread out over a surface, followed by a stepof “consolidating” the structure obtained.

According to an advantageous embodiment of the invention, the“web-forming” step is carried out “dry” (“drylaid” process), for examplestarting in particular with fibres of the invention having a length ofbetween 40 and 80 mm. The fibres may, for example, be treated using anordinary carding machine.

According to another advantageous embodiment of the invention, the“web-forming” step is carried out “wet” or by “papermaking means”(“wetlaid” process). The fibres used in this embodiment generally have alength of between 2 and 12 mm, preferably between 3 and 7 mm, and theirlinear density, expressed in decitex, is generally between 0.5 and 20.Theoretically, it is possible to use fibres having a length greater than12 mm, but in practice longer fibres entangle, requiring a larger amountof water, thereby making the process more expensive and morecomplicated.

According to this embodiment, the non-woven article is obtained byintroducing the various constituents of the article into the water,namely the fibres and a fibrous bonding agent composed of a pulp basedon a synthetic polymer having a thermal withstand greater than or equalto 180° C. (such as a para-aramid pulp) and/or fibrids based on asynthetic polymer having a thermal withstand greater than or equal to180° C. and/or fibrids according to the invention, and optionally otherdesirable adjuvants, additives or fillers.

The pulp based on a synthetic polymer possessing a thermal withstandgreater than or equal to 180° C. is generally obtained from fibres ofusual length, especially fibrils, in a manner known per se, in order togive it a large number of catching points and thus increase its specificsurface area. Among synthetic fibres, only highly crystallized fibresmay be fibrilized. This is the case with completely aromatic polyamidesand polyesters, but other highly crystallized polymers are able to besplit along the fibre axis or are fibrilizable.

To improve certain properties, adjuvants, additives or fillers may alsobe used in various proportions depending on the desired properties; forexample, mica may be introduced in order to further increase thedielectric properties of the article.

The “papermaking method” of preparing non-woven articles is known tothose skilled in the art.

The step of “consolidation” of the structure obtained by web forming, asdescribed above, may be carried out according to any method known tothose skilled in the art. Preferably, the “consolidation” is carried outthermally, for example by thermal pressing of the article. The thermalpressing temperature is generally greater than the glass transitiontemperature of the thermoplastic polymer of the fibres and/or fibridsaccording to the invention contained in the article. Preferably, thethermal pressing temperature is between the glass transition temperatureand the softening temperature of the thermoplastic polymer.

According to one advantageous embodiment of the invention, the thermalpressing temperature is between 200 and 350° C. Preferably, the pressureis greater than or equal to 5 bar.

This pressing densifies and consolidates the article of the invention.It is generally accompanied by plastic flow of the thermoplastic polymerof the fibres and/or fibrids according to the invention contained in thearticle through the structure of the article.

There is no limitation imposed as to the way in which the thermalpressing is carried out. Any means of thermally pressing a non-wovenarticle may be used.

For example, the pressing may be carried out using a press or a calenderwith heated rolls. It is possible to carry out several passes on thepressing apparatus so as to obtain the desired density.

The preferred thermal pressing method of the invention is calendering.

According to a particular embodiment of the invention, the thermalpressing is carried out using a continuous press.

The articles obtained by this pressing are various and varied dependingon the thermal pressing conditions employed—especially the pressingtemperature, pressure and time—and depending on the formulation of thearticle—especially the amount of fibres and/or fibrids according to theinvention contained in the article and the amount of thermoplasticpolymer present in these fibres and/or fibrids.

These parameters are chosen according to the type of article and thedesired properties of this article.

The articles of the invention may be used especially in the electricalinsulation field.

The role of the articles varies depending on their density and thereforeon their strength/dielectric properties. They may, for example, be usedin an insulation system, in which the main insulant is an oil or aresin, as a mechanical “spacer” or “reinforcement” to be insertedbetween two parts to be electrically isolated. The articles may also beused directly as insulant in insulation systems of the “dry” type.

The invention also relates to a fibre characterized in that it is formedfrom a polymer blend comprising at least:

-   -   A thermally stable polymer; and    -   A thermoplastic polymer chosen from the group of polysulphides        and polysulphones;        and in that it has a linear density of less than or equal to        13.2 dtex.

The invention also relates to a fibrid, characterized in that it isformed from a polymer blend comprising at least:

-   -   A thermally stable polymer; and    -   A thermoplastic polymer chosen from the group of polysulphides        and polysulphones.

Everything described relating to the thermally stable polymer, thethermoplastic polymer, the fibres and fibrids of the articles of theinvention, the process for obtaining the fibres and the process forobtaining the fibrids applies here in the same way for the fibres andfibrids of the invention above.

The invention also relates, in a third subject, to the use of thearticles of the invention as described above in the electricalinsulation field.

Further details and advantages of the invention will become more clearlyapparent in the light of the examples described below.

EXAMPLES Examples 1 to 3 Preparation of the ThermopolasticPolymer/Thermally Stable Polymer Blend Example 1

180 kg of DMEU solvent were introduced into a heated and stirredreactor. This solvent was firstly heated to a temperature of between 60°C. and 120° C. The PESU polymer (MW: 80 000 to 90 000 g/mol) in the formof lenticular granules was introduced into the hot solvent, in ten equalfractions. The time required between each fraction depended on theintensity of the stirring and the temperature. The polymer wasintroduced until it represented 20 to 40% by weight of the blend.

The polymer content in the solution influences its viscosity. As anexample, at 21% the viscosity at 25° C. is 350 poise; at 28% theviscosity is 460 poise.

The PESU thermoplastic polymer was blended with the Kermel®polyamide-imide by melt blending, between 60 and 120° C., the blenddescribed above containing the PESU and a 21 wt % solution of Kermel®polyamide-imide in the DMEU solvent (MW: 150 000 g/mol (polystyreneequivalent); viscosity: 600 poise at 25° C.). The proportion of the twosolutions in the blend was expressed as the proportion of PESU polymerin the dry matter and was between 40 and 60%.

Example 2

A Kermel® polyamide-imide/PESU blend was obtained directly by dissolvingthe PESU polymer in a 13 wt % solution of Kermel® polyamide-imide in theDMEU solvent using a blender having a high shear rate and a high degreeof recycling.

Example 3

A mixture containing the PESU was prepared according to the operatingmethod of Example 1. The blend with the Kermel® polyamide-imide (in theform of a 21 wt % solution of Kermel® polyamide-imide in the DMEUsolvent) was produced during the spinning, by conjointly injecting thetwo solutions into a common line, upstream of the static mixersinstalled in this line, which feeds the spinning unit. The proportionsof the two solutions in the blend is respected by adjusting the rotationspeeds of metering pumps.

Examples 4 and 5 Spinning of Thermoplastic Polymer/Thermally StablePolymer Blends Example 4

The PESU/Kermel® polyamide-imide blends of Examples 1 to 3 were spunusing a wet spinning process. The proportion of PESU polymer was 40% byweight. The conditions below represent, as examples, the spinningparameters used:

-   -   Dies: 10 000 holes 50 μm in diameter    -   Coagulation bath: 55% solvent, 19° C.    -   Spinning rate: 14 m/min    -   Draw ratio: 2×    -   Final linear density obtained: 4.4 dtex.

The fibre was dried, crimped and chopped conventionally (fibre length:60 mm).

Example 5

The PESU/Kermel® polyamide-imide blends of Examples 1 to 3 were spunusing a wet spinning process. The proportion of PESU polymer was 50%.The conditions below represent, as examples, the spinning parametersused:

-   -   Dies: 10 000 holes 40 μm in diameter    -   Coagulation bath: 60% solvent, 19° C.    -   Spinning rate: 14 m/min    -   Draw ratio: 2×    -   Final linear density obtained: 2.2 dtex.

The fibre was dried conventionally. The crimping and chopping werecarried out conventionally.

Examples 6 to 8 Articles

Non-woven articles of various grammages were prepared from the fibres ofExample 4 using the “dry method” and by “consolidation” (carding, webforming, calendering) according to a method known to those skilled inthe art.

The equipment employed was the following:

-   -   parallel-output Garnett®-type carding machine;    -   Asselin® web former;    -   KTM® calender.

Table 1 describes the operating conditions used and the characteristicsof the articles obtained. The mechanical properties—strength andelongation at break—were measured according to the NF-EN 29073-3standard of December 1992. The thickness of the articles was measuredusing a Palmer®-type micrometer.

TABLE 1 Examples Example 6 Example 7 (*) Example 8 Calendering rate 5 55 (m/min) Calendering 250 250 270 temperature (° C.) Calenderingpressure 6 6 6 (bar) Grammage (g/m²) 42 60 65 Thickness (μm) 50 65 70Density (g/cm³) 0.84 0.92 0.93 Machine direction 20.2 41 60.9 tensilestrength (N/5 cm) Machine direction 1.4 2.1 2.9 elongation at break (%)(*) the article according to Example 7 was subjected to two calenderingpasses.

The plastic flow and the density obtained after calendering wereobserved.

Examples 9 to 12 Preparation of Fibrids from a ThermoplasticPolymer/Thermally Stable Polymer Blend

The PESU/Kermel® polyamide-imide blend of Example 1, diluted with DMEUin order to obtain the desired concentration of PESU/Kermel®polyamide-imide polymers, was precipitated under high shear using amethod as described in the documents FR 1214 126 or U.S. Pat. No.4,187,143, in an aqueous coagulation bath having a given concentrationof DMEU solvent. Table 2 gives the conditions for preparing the fibrids.

TABLE 2 Proportion of PESU/ Kermel ® Proportion of the polyamide-imideby solvent in the weight (%) before coagulation bath by Examplesprecipitation weight (%) 9 9.5 25 10 15 50 11 9.5 0 12 9.5 50

The characteristics of the fibrids were measured on the MORFI apparatus(conventional apparatus for measuring papermaking cellulose fibres).Table 3 gives these characteristics.

TABLE 3 Examples 9 10 11 12 Length (mm) 0.315 0.431 0.351 0.289 Width(μm) 40.2 44.6 49.7 30.3 Fine elements (% by 19.5 11.0 14.7 24.9 length)Amount of fine 1.6 0.4 0.6 3.6 elements (% by area)

Examples 13 to 16 Articles Obtained from Fibrids

The fibrids of Examples 9 to 12 were blended with an equal weight ofKermel® polyamide-imide fibres 6 mm in length. These four preparationswere used to produce papers on a Frank-type handsheet apparatus by wetprocessing and according to a conventional papermaking process. Theintended weight of the specimens was 80 g/m². The characteristics of thepapers are given in Table 4.

The retention factor was defined as follows:Retention factor (%)=(1−[(mass introduced (g)−mass after passing through(g))/mass introduced (g)]×100.

TABLE 4 Mass Mass after introduced passing Thickness into the throughthe Retention in apparatus apparatus factor Grammage Hand ExamplesFibrids μm (g) (g) (%) (g/m²) (cm³/g) 13 Ex. 9 199.6 2.506 2.448 98 772.6 14 Ex. 10 238.8 2.516 2.478 98 81 2.9 15 Ex. 11 199.5 2.517 2.342 9374 2.7 16 Ex. 12 191.3 2.525 2.500 99 77 2.5

After drying, the papers obtained were characterized by their mechanicalproperties (Table 5) and by their air permeability in the Bendtsenapparatus at a pressure of 1.47 kPa (Table 6) using the conventionalmethods of the papermaking industry.

TABLE 5 Mechanical strength of the papers Examples 13 14 15 16 Breakingforce (N) 1.78 2.37 1.05 3.23 Tensile strength 119 158 70 216 (N/m)Tensile strength 1.55 1.95 0.94 2.84 index (Nm/g) Elongation at 1.892.61 1.16 2.09 break (%) Elastic modulus 558 370 638 632 (MPa) Tearstrength (mN) 820 1600 560 1400 Tear Index (Nm/g) 3.27 6.07 2.32 5.6

TABLE 6 Air permeability Examples 13 14 15 16 Mean (ml/min) 50.5 58.7876.8 1.4 Standard 4.9 124.9 0.2 deviation

Examples 17 to 24 Hot-Pressed Articles Obtained from Fibrids

The papers of Examples 13 to 16 were hot-pressed in a laboratory platenpress at 280° C.:

either for 10 min at 100 bar

or for 5 min at 200 bar.

TABLE 7 Thickness of the pressed papers Examples 17 18 19 20 Pressure:Article Ex. 13 Ex. 14 Ex. 15 Ex. 16 100 bar Mean thickness 125.8 137.3125.7 121.5 (μm) Hand (cm³/g) 1.63 1.69 1.69 1.57 Examples 21 22 23 24Pressure: Article Ex. 13 Ex. 14 Ex. 15 Ex. 16 200 bar Mean thickness123.1 122 116.4 121.4 (μm) Hand (cm³/g) 1.59 1.50 1.57 1.58

1. A non-woven article comprising fibers formed from a polymer blendcomprising a polyethersulphone and an aromatic polyamide-imide, saidarticle having a density in the range of about 0.84 to about 0.93, atensile strength in the machine direction of about 20.2 to about 60.9N/5 cm, and an elongation at break of about 1.4 to about 2.9%. 2.Electrical insulation comprising the non-woven article of claim 1.